The purpose of this proposal is to provide descriptive and analytic population-based data on the occurrence of and risk factors for mental retardation in Rochester, Minnesota, from 1960 through 1984. The study will extend and complete an ongoing mental retardation project covering 1960-1964. All medical and school records will be reviewed. This information will then provide incidence rates and secular trends for mental retardation for the periods of the study. A case-control analysis of the cohort will be done to identify risk factors associated with an increased risk for mental retardation, including prenatal, perinatal, and postnatal events. Long-term follow-up of the cases for comparative morbidity, mortality, and length of survivorship will also be provided.